Cellular Base Station Antennas typically contain one or more columns of radiating elements connected by a power distribution feed network. This feed network contains power dividers that split the input power between groups of radiating elements or sub-arrays of radiating elements. The feed network also is designed to generate specific phase values at each radiating element or sub-array of radiating elements. This feed network may also contain a phase shifter which allows the phases for each radiating element or sub-array of radiating elements to be adjusted so as to adjust the beam peak position of the main beam of the antenna pattern.
One standard for wireless communication of high-speed data for mobile phones and data terminals is known as Long-Term Evolution, commonly abbreviated as LTE and marketed as 4G LTE. The LTE standard supports both Frequency Division Duplexing (FDD-LTE) and Time Division Duplexing (TD-LTE) technologies in different sub-bands. For example the 2490-2690 MHz band is licensed world-wide for TD-LTE. In many of these same countries, bands such as 1710-1880, 1850-1990, 1920-2170 and 1710-2155 MHz are used for FDD-LTE applications.
Ultra-wideband radiating elements than operate in a band of 1710 MHz to 2690 MHz are available. However, different Multiple Input Multiple Output (MIMO) configurations are encouraged for use in the different sub-bands. Many TD-LTE networks make use of multi-column beamforming antennas. An antenna optimized for TD-LTE may include 4 columns of radiators spaced 0.5-0.65 wavelength apart and each generating a nominal column Half Power Beamwidth (HPBW) of about 65 to 90 degrees in the 2490-2690 MHz band. This results in a 4×1 MIMO antenna. In contrast, in FDD-LTE applications, 2×1 MIMO is encouraged, using 2 columns of radiators with a nominal 45-65 degree HPBW and a column spacing of about one wavelength. Due to these different requirements concerning the number of MIMO ports and column spacing, 4×1 MIMO and 2×1 MIMO are typically implemented in separate antennas.
Attempts to combine sub-bands in common radiating element arrays are known. For example, using broadband radiating elements and then placing multiplexer filters (e.g. diplexers, triplexers) between the radiating elements and the rest of the feed network in order to allow multiple narrower band frequency-specific feed networks to be attached to the same array of radiating elements is disclosed in U.S. patent application Ser. No. 13/771,474, filed Feb. 20, 2013, which is incorporated by reference herein. This sharing of radiating elements allows, for example, a single column of radiating elements to generate patterns with independent elevation downtilts for two different frequency bands. This concept in principle may be extended to antennas with multiple columns of radiating elements. However, in practice, if the number of columns and column spacing are optimized for one sub-band of LTE, number of columns and column spacing will not be optimized for the other sub-bands of LTE. For example, a design that is optimized for the FDD-LTE 1900 MHz sub-band (two columns at about one wavelength apart) results in a sub-optimal configuration for the TD-LTE sub-band (2 columns at about 1.3 wavelength separation, where four columns at 0.65 wavelength is desired).
Azimuth pattern variation is another issue that exists with respect to ultra-wideband antennas. For example in the wireless communications market there is a need for an antenna that generates independent patterns in the 1710-2170 MHz and 2490-2690 MHz bands. Radiating elements covering the entire 1710-2690 MHz band are known. However since 1710-2690 MHz is a 42% band (i.e., the width of the band is 42% of the midpoint of the band), a multi-column array generating a narrow HPBW of, for example 33 to 45 degrees, will experience 42% variation in azimuth HPBW across this band. This amount of variation is unacceptable for many applications.